There is demand to reduce the operator control effort on fork lift trucks, for example by the reduction or elimination of the service brake effort, which taxes the drivers with continual brake applications during normal operation. Furthermore, park brake levers may wear out and require regular maintenance. By augmenting or replacing the service brakes and/or the parking brakes with clutch pack braking, the above issues regarding operator effort and brake maintenance may be addressed.
Conventional drive axle differentials apply approximately equal driving torque to the drive wheels, for example during tight turns. This tends to force the truck to drive straight forward applying extra loads to the drive train, inside drive tire, and steer tires, which robs power from the hydraulic system during hoisting, wastes fuel and adds to the driver's steering effort. Transmission systems that include clutch packs in the drive axle include separate service brakes, separate park brake and a differential. See, for example, U.S. Pat. No. 7,090,608. Other transmission arrangements that disconnect the engine while providing clutch pack braking also include service brakes, a park brake system and a differential.
The present invention addresses these and other problems.